Tackling The Hazard Of Head Checks In Rails

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1、TacklingTheHazardOfHeadChecksInRailsInternationalRailwayJournal,June,1999byIngMartinHiensch,IngJeroenSmuldersRollingcontactfatiguecrackpropagationisoftendeflectedverticallyandisthereforepotentiallyhazardousasacauseofrailfailure.Earlyidentificationwillenablec

2、orrectivemeasurestobetaken.THETERM"headchecks"isusedtorefertoatypeofcrackinginrailsthatoccursparticularlyoncurves(Figure1).Asaresultofexcessivelocalisedplasticdeformationoftherailhead,whichoccursinresponsetoincreasingshearforcesanddecreasingcontactareabetwee

3、nthewheelandtherail,smallcracksappearinthecontactarea.Intime,thesecrackspropagatefurtherintherailhead.Ourpresentstudydealsinparticularwithcrackpropagationafterinitiation.Examinationandidentificationofalargenumberofcracksinpracticehaveyieldedanunderstandingof

4、thevariouscrackpropagationstages.Wehaveattemptedtodevelopatheorytoexplainthecrackingprocess.Wediscoveredthatheadcheckspropagateinaverticaldirectionmuchmorefrequentlythanpreviouslyassumed,whichispotentiallyhazardouswithregardtorailfailure.Acriticallimitvaluew

5、asidentifiedatwhichverticalpropagationsuddenlyoccurs.Thisperceptionunderpinsthetheoreticalpropositionthatstickingofthecracksurfaceshasamajorinfluenceonthedirectionofcrackpropagation.Lubricationofrailsseemstoencourageverticalpropagation.Theloadingontrackshasi

6、ncreasedsubstantiallyinrecentyearsbecauseofanincreaseintrainspeeds,higheraxleloadsandchangesinbogiedesigns.Techniquessuchasheadhardeninghavebeenunabletopreventincreasingdamagetodate,particularlyonswitchesandcurves.Thistypeoffault,whichinitiatesintherunningsu

7、rfacebetweenthewheelandtherail,istermedrollingcontactfatigue滚动接触疲劳.In-depthresearchhasalreadybeencarriedoutnationallyandinternationally(ERRID173)intothecauseofthistypeofdamage.Butthereremainunresolvedquestionsoncrackdevelopment,criticalcracksize,andthedetect

8、ion,combatingandpreventionofsuchfaults.NSRailinfrabeheer'sSystemDevelopmentDepartment(responsiblefortrackandstructures)andtheMaterialsScienceDepartmentofNSTechnicalResearch,whicharebothpartofNet